How are you using the stock? I ask because if you will still be able distinctly to taste the stock itself, e.g., in a traditional chicken noodle soup, may I respectfully suggest that you make sure the people eating it are not going to mind (if you care about such things). The gizzards will profoundly affect the taste of the stock. And if ever there were a divider food, gizzards would be it. Some people love them. Others (and I am among them) don't care for the taste at all, and although I would never say anything if served such a soup, I'd wish you'd left them out. ;o)

Yeah, I have to wonder if the people who don't like gizzards had stock that had liver in it - liver is known to give the stock a funky flavor. I've never noticed anything odd from the rest of the gizzards, though. Just more yummy chicken flavor.

I have tasted stock made with just the heart and gizzards, and not the liver, so I can affirm that the problem does lie with the gizzard and heart. What's a "yummy chicken flavor" to some is a "Bleeh, did you really have to?" to others. ;o)

As a child when visiting my grandmothers, I was involved with butchering the bird for dinner. When I look at the purpose of the gizzard in a bird, it is like a filter for what the bird has eaten. The gizzard has the stones that grind, which to me give that mineral taste. Don't know why I don't care for the heart, and it may also be that is muscle which pumps and filters.